part of my model are see through
This usally happens when normals are facing the wrong side of the mesh

Using the backface culling  in the N panel will make the concerned faces transparent (see-through as in your UE4 game engine)

You can check your faces normals with this option in the N panel. This will show you the normals in the viewport.
  

To make the normals consistent go in Edit Mode with Tab, select all with A (only the bad faces could be enough), and use Ctrl+N (recalculate), or  Shift+Ctrl+N (recalculate the other direction), or select the faces and click Flip directions